Vehicle speed control system

ABSTRACT

A vehicle speed control system for controlling a vehicle having a plurality of wheels. The vehicle speed control system is configured to automatically control the speed of the vehicle in dependence on an input target set-speed. The system carries out a method that includes: applying torque to at least one of the plurality of wheels; receiving a user input of a target set-speed at which the vehicle is intended to travel; and applying torque to the at least one of the plurality of wheels for propelling the vehicle at a vehicle control speed. The system further controls the vehicle control speed as a function of at least one of the instantaneous vehicle speed and the terrain over which the vehicle is travelling.

FIELD OF THE INVENTION

The invention relates to a system for controlling the speed of avehicle. In particular, but not exclusively, the invention relates to asystem for controlling the speed of a land-based vehicle which iscapable of driving in a variety of different and extreme terrains andconditions, in particular in off road conditions.

BACKGROUND TO THE INVENTION

In known vehicle speed control systems, typically referred to as cruisecontrol systems, the vehicle speed is maintained once set by the userwithout further intervention by the user so as to improve the drivingexperience for the user.

The user selects a speed at which the vehicle is to be maintained, andthe vehicle is maintained at that speed for as long as the user does notapply a brake or, in some cases, the clutch. The cruise control systemtakes its speed signal from a driveshaft or wheel speed sensors. Whenthe brake or the clutch is depressed, the cruise control system isdisabled so that the user can change the vehicle speed withoutresistance from the system. If the user depresses the accelerator pedalthe vehicle speed will increase, but once the user removes his foot fromthe accelerator pedal the vehicle reverts to the pre-set cruise speed.

More sophisticated cruise control systems are integrated into the enginemanagement system and may include an adaptive functionality which takesinto account the distance to the vehicle in front using a radar-basedsystem. For example, the vehicle may be provided with a forward-lookingradar detection system so that the speed and distance of the vehicle infront is detected and a safe following speed and distance is maintainedautomatically without the need for user input. If the lead vehicle slowsdown, or another object is detected by the radar detection system, thesystem sends a signal to the engine or the braking system to slow thevehicle down accordingly.

Such systems are usually operable only above a certain speed, typicallyaround 15 mph, and are ideal in circumstances in which the vehicle istravelling in steady traffic conditions, and particularly on highways ormotorways. In congested traffic conditions, however, where vehicle speedtends to vary widely, cruise control systems are ineffective, andespecially where the systems are inoperable because of a minimum speedrequirement. A minimum speed requirement is often imposed on cruisecontrol systems so as to reduce the likelihood of low speed collision,for example when parking. Such systems are therefore ineffective incertain driving conditions (e.g. low speed) and are set to beautomatically disabled in circumstances in which a user may not considerit to be desirable to do so. Known systems also cancel out of speedcontrol upon detection of a vehicle wheel slip event.

It is also known to provide a control system for a motor vehicle forcontrolling one or more vehicle subsystems. U.S. Pat. No. 7,349,776, thecontent of which is hereby incorporated by reference, discloses avehicle control system comprising a plurality of subsystem controllersincluding an engine management system, a transmission controller, asteering controller, a brakes controller and a suspension controller.The subsystem controllers are each operable in a plurality of subsystemfunction modes. The subsystem controllers are connected to a vehiclemode controller which controls the subsystem controllers to assume arequired function mode so as to provide a number of driving modes forthe vehicle. Each of the driving modes corresponds to a particulardriving condition or set of driving conditions, and in each mode each ofthe sub-systems is set to the function mode most appropriate to thoseconditions. Such conditions are linked to types of terrain over whichthe vehicle may be driven such as grass/gravel/snow, mud and ruts, rockcrawl, sand and a highway mode known as ‘special programs off’ (SPO).The vehicle mode controller may be referred to as a Terrain Response®(TR) system or controller.

In co-pending patent application GB1314727.7, the entire contents ofwhich are incorporated herein by reference a speed control systemsuitable for controlling the speed of a vehicle at lower speeds, inparticular in off road environments is disclosed. This system uses theapplication of positive and negative torque to control the speed of avehicle and contrary to known systems does not cancel the speed controlfunction if a slip event is detected at one or more wheels, but insteadmanages the torque at the wheels to control the slip event and maintainprogress of the vehicle. This type of system, or similar systems forcontrolling the speed of a vehicle is referred to herein as Low SpeedProgress control (LSP)

The present invention seeks to improve upon the control of speed inoff-road conditions, in particular when the vehicle is required toovercome obstacles.

SUMMARY OF THE INVENTION

Embodiments of the invention may be understood with reference to theappended claims.

Aspects of the present invention provide a system, a vehicle and amethod.

According to a first aspect of the present invention, for whichprotection is sought, there is provided a vehicle speed control systemfor a vehicle having a plurality of wheels, the vehicle speed controlsystem is configured to automatically control the speed of the vehicleto a vehicle control speed in dependence on an input target set-speed,the vehicle speed control system comprising: means for receiving a userinput of a target set-speed at which the vehicle is intended to travel;means for applying torque to the at least one of the plurality of wheelsfor propelling the vehicle at the vehicle control speed; and means forcontrolling the vehicle control speed as a function of at least one ofthe instantaneous vehicle speed and the terrain over which the vehicleis travelling.

The various means comprising the invention may be embodied in electricalcontrollers. Each means may comprise an individual controller, maycomprise a functional block within a multi-functional controller, or maycomprise functional blocks within existing electronic controllers of thevehicle.

In this way the rate at which the speed to which the vehicle iscontrolled is limited in dependence upon the instantaneous speed of thevehicle. This can have significant benefits for the composure of thevehicle when driving off road.

One particular situation in which the vehicle speed control system isadvantageous is when, for example, the vehicle is at a stand-stillagainst an object, for example a log, curb, boulder etc. If the userturns on a low speed progress control (LSP), the vehicle may not beginto move immediately as a result of the torque build up required toovercome the object. The driver may then assume that LSP is not workingor is unable to overcome the object without their intervention, and thenattempt to force the vehicle to move by pressing a set + button toincrease the LSP set speed to start the vehicle moving. Without thebenefit of the disclosed vehicle speed control system it is possiblethat as a large amount of torque is needed to overcome the object, onceit is overcome the vehicle may accelerate quickly as it attempts toreach its set speed, which the user has set higher than intended whilstwaiting for the torque at the wheels to be sufficient to overcome theobstacle. This may lead to a reduction in vehicle composure.

In another scenario, if the driver has previously been driving with LSPswitched on and has placed the LSP in a standby mode prior to slowingthe vehicle to a standstill, if the driver presses a “resume” button ofthe LSP system to resume automatic speed control under LSP, depending onthe previously set LSP set speed the effect may be the same as describedabove. This may be exasperated when driving over varied terrain, wherethe previously set LSP set speed may have been appropriate forrelatively smooth terrain, but uncomfortable for rough terrain.

The means for propelling the vehicle at the vehicle control speed mayinclude: means for determining a current speed at which the vehicle istravelling; means for comparing the current speed with the vehiclecontrol speed and for providing an output indicative of the differencebetween the current speed and the vehicle control speed; and means forevaluating the torque to be applied to at least one of the vehiclewheels in dependence on said output and outputting a torque requestsignal in dependence thereon.

The vehicle control system may comprise a means of reducing the vehiclecontrol speed as a function of the torque request signal. Said means forreducing the vehicle control speed as a function of the torque requestsignal may be configured to reduce said vehicle control speed as afunction of the torque request signal if the instantaneous vehicle speedis less than a prescribed value. In one embodiment the prescribed valueis in the range of 0 to 3 kilometers per hour.

In this manner where there is a large torque request combined with, forexample a low speed (as would be the case when the vehicle is attemptingto overcome an obstacle in its path), once the obstacle is overcome, asthe vehicle control speed is controlled further in dependence on thetorque request signal, i.e. it is limited to a lower value than theinput target set-speed, the full torque at the wheels does not attemptto accelerate the vehicle immediately towards the target set-speed, butinstead accelerates towards a lower vehicle control speed. As lessacceleration is required to achieve this lower vehicle control speed,and as acceleration is controlled by vehicle torque request, as thevehicle control speed will be much closer to the current vehicle speedthe torque request will reduce quickly (as less acceleration isrequired) and prevent loss of composure.

The means for controlling the vehicle control speed may be configured tocontrol said vehicle control speed as a function of the terrain overwhich the vehicle is travelling in dependence on a signal indicative auser selected terrain mode.

Alternatively the means for controlling the vehicle control speed may beconfigured to control said vehicle control speed as a function of theterrain over which the vehicle is travelling in dependence on a signalindicative a terrain mode automatically selected in dependence on sensedvehicle and/or environmental parameters.

In particular, when the vehicle is driving on rough surfaces, if theuser attempts to increase the target set-speed to a value which, if thedriver is inexperienced, may set be inappropriate to the terrain overwhich the vehicle is travelling. By inappropriate it is meant that theuser input target set-speed may be such that vehicle composure isaffected.

Automatically controlling the speed of the vehicle to a vehicle controlspeed in dependence on an input target set-speed may further comprise:means for limiting the maximum input target set-speed in dependence uponsaid at least one of the instantaneous vehicle speed and the terrainover which the vehicle is travelling.

By applying a variable limit to the maximum set-speed value that theuser can input the system may use the set-speed as the vehicle controlspeed. A signal can then be output to the user, for example via an HMI,to indicate to the user that the target set-speed has been temporarilycapped. This may have additional educational benefit to the driver as toappropriate vehicle speeds in certain driving conditions.

Optionally limiting the maximum input target set-speed may comprise thesystem defining a maximum Δ V_set in dependence upon said at least oneof the instantaneous vehicle speed and the terrain over which thevehicle is travelling, where Δ V_set is the difference between anexisting target set-speed, and a new user input target set-speed. Themaximum value of Δ V_set may be reduced in dependence upon theinstantaneous torque being applied to the at least one of the pluralityof wheels.

It will be appreciated that values such as Δ V_set that are determinedin dependence on specific conditions or parameters may be calculated bymeans of an algorithm, or alternatively the correlations may begenerated either theoretically or empirically and stored in look uptables stored in a memory means of the system and recoverable therefromfor use by the system

The vehicle speed control system may further comprise means to reducethe target set-speed in dependence upon the vehicle control speed, inparticular in the circumstance wherein a target set speed already existsin the system and the driver presses the resume button when attemptingto overcome an obstacle.

In this manner if the control system determines that the vehicle controlspeed should be less than the target set-speed, it can reduce the targetset-speed. The target set-speed may be reduced to the control speed. Inthis manner the speed to which the vehicle is controlled is manipulatedby changing the target set-speed, and then controlling to that targetset speed. This allows the vehicle to continue to control to the targetset-speed, but allows for the target set-speed to be manipulated whereappropriate without direct intervention by the user.

Optionally the target set-speed may be reduced to:vehicle control speed+ΔV_set_maxwherein Δ V_set_max defines a maximum value by which the targetset-speed is allowed to exceed the control speed at a given vehiclespeed and/or terrain.

This allows the target set-speed to be reduced so that it is within theallowable margin of the control speed. In this manner the actual targetset-speed may be automatically reduced and once the obstacle isovercome, the user can then increase the target set-speed if desired. Inthis manner, not only is the vehicle control speed reduced whenappropriate but as the target set-speed is also reduced, after the eventcausing the reduction of the vehicle control speed has passed, apositive input is required by the user to confirm their desire toaccelerate the vehicle above the maximum target set-speed deemedappropriate during the event in question. This allows additional timefor the driver to retain assess the prevailing conditions and preventsthe vehicle immediately resuming the pre-event target set-speed to thedetriment of vehicle composure.

According to a further aspect of the invention, for which protection issought, there is provided a control system for a vehicle having aplurality of wheels, the control system configured to automaticallycontrol the speed of the vehicle in dependence on an input targetset-speed and comprising: means for receiving a user input of a targetset-speed at which the vehicle is intended to travel comprising an inputmeans to enable the user to incrementally increase or decrease thetarget set-speed; means for applying torque to the at least one of theplurality of wheels for propelling the vehicle at the vehicle controlspeed; and wherein the means for receiving a user input of a targetset-speed is configured to increase or decrease the target set speedupon each actuation of said input means by an incremental value, andwherein the control system is configured to determined said incrementalvalue in dependence upon at least the terrain over which the vehicle istravelling.

The control system may further comprise a terrain mode selectioninterface for receiving a user input of the terrain over which thevehicle is travelling, and wherein said incremental value is dependentupon a signal indicative of the terrain mode selected by the user.Alternatively the control system may further comprising an automaticterrain mode selection means comprising a plurality of vehicle and/orenvironmental sensors and configured to selecting an automatic terrainmode in dependence upon said vehicle and/or environmental sensors, andwherein said incremental value is dependent upon a signal indicative ofthe automatically selected terrain mode.

The control system may be configured to further determine saidincremental value further in dependence upon one of: the speed at whichthe vehicle is travelling; and the target set-speed, for example thelower the speed at which the vehicle is travelling or the lower thetarget set-speed, the smaller the incremental value may be.

The invention also provides a vehicle having a system as describedhereinabove.

According to a further aspects of the invention for which protection issought there are provided methods for performing the functionality ofthe system and a memory device which comprises a carrier medium carryinga computer-readable code for controlling the vehicle to carry out themethod described below.

It will be appreciated that preferred and/or optional features of anyone aspect of the invention may be incorporated alone or in appropriatecombination within the any other aspect of the invention also.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to the following figures in which:

FIG. 1 is a schematic illustration of a vehicle according to anembodiment of the invention in plan view;

FIG. 2 shows the vehicle of FIG. 1 in side view;

FIG. 3 is a high level schematic diagram of an embodiment of the vehiclespeed control system of the present invention, including a cruisecontrol system and a low-speed progress control system;

FIG. 4 is a schematic diagram of further features of the vehicle speedcontrol system in FIG. 3;

FIG. 5 illustrates a steering wheel and brake and accelerator pedals ofa vehicle according to an embodiment of the present invention;

FIG. 6 is a flowchart illustrating operation of a vehicle according toone embodiment of the present invention; and

FIG. 7 is a flowchart illustrating operation of a vehicle according toanother embodiment of the present invention.

DETAILED DESCRIPTION

References herein to a block such as a function block are to beunderstood to include reference to software code for performing thefunction or action specified which may be an output that is providedresponsive to one or more inputs. The code may be in the form of asoftware routine or function called by a main computer program, or maybe code forming part of a flow of code not being a separate routine orfunction. Reference to function block is made for ease of explanation ofthe manner of operation of embodiments of the present invention.

FIG. 1 shows a vehicle 100 according to an embodiment of the presentinvention. The vehicle 100 has a powertrain 129 that includes an engine121 that is connected to a driveline 130 having an automatictransmission 124. It is to be understood that embodiments of the presentinvention are also suitable for use in vehicles with manualtransmissions, continuously variable transmissions or any other suitabletransmission.

In the embodiment of FIG. 1 the transmission 124 may be set to one of aplurality of transmission operating modes, being a park mode, a reversemode, a neutral mode, a drive mode or a sport mode, by means of atransmission mode selector dial 124S. The selector dial 124S provides anoutput signal to a powertrain controller 11 in response to which thepowertrain controller 11 causes the transmission 124 to operate inaccordance with the selected transmission mode.

The driveline 130 is arranged to drive a pair of front vehicle wheels111,112 by means of a front differential 137 and a pair of front driveshafts 118. The driveline 130 also comprises an auxiliary drivelineportion 131 arranged to drive a pair of rear wheels 114, 115 by means ofan auxiliary driveshaft or prop-shaft 132, a rear differential 135 and apair of rear driveshafts 139.

Embodiments of the invention are suitable for use with vehicles in whichthe transmission is arranged to drive only a pair of front wheels oronly a pair of rear wheels (i.e. front wheel drive vehicles or rearwheel drive vehicles) or selectable two wheel drive/four wheel drivevehicles. In the embodiment of FIG. 1 the transmission 124 is releasablyconnectable to the auxiliary driveline portion 131 by means of a powertransfer unit (PTU) 131P, allowing operation in a two wheel drive modeor a four wheel drive mode. It is to be understood that embodiments ofthe invention may be suitable for vehicles having more than four wheelsor where only two wheels are driven, for example two wheels of a threewheeled vehicle or four wheeled vehicle or a vehicle with more than fourwheels.

A control system for the vehicle engine 121 includes a centralcontroller 10, referred to as a vehicle control unit (VCU) 10, thepowertrain controller 11, a brake controller 13 and a steeringcontroller 170C. The brake controller 13 forms part of a braking system22 (FIG. 3). The VCU 10 receives and outputs a plurality of signals toand from various sensors and subsystems (not shown) provided on thevehicle. The VCU 10 includes a low-speed progress (LSP) control system12 shown in FIG. 3 and a stability control system (SCS) 14. The SCS 14improves the safety of the vehicle 100 by detecting and managing loss oftraction. When a reduction in traction or steering control is detected,the SCS 14 is operable automatically to command a brake controller 13 toapply one or more brakes of the vehicle to help to steer the vehicle 100in the direction the user wishes to travel. In the embodiment shown theSCS 14 is implemented by the VCU 10. In some alternative embodiments theSCS 14 may be implemented by the brake controller 13. Furtheralternatively, the SCS 14 may be implemented by a separate controller.

Although not shown in detail in FIG. 3, the VCU 10 further includes aDynamic Stability Control (DSC) function block, a Traction Control (TC)function block an Anti-Lock Braking System (ABS) function block and aHill Descent Control (HDC) function block. These function blocks areimplemented in software code run by a computing device of the VCU 10 andprovide outputs indicative of, for example, DSC activity, TC activity,ABS activity, brake interventions on individual wheels and engine torquerequests from the VCU 10 to the engine 121 in the event a wheel slipevent occurs. Each of the aforementioned events indicate that a wheelslip event has occurred. Other vehicle sub-systems such as a rollstability control system or the like may also be useful.

As noted above the vehicle 100 also includes a cruise control system 16which is operable to automatically maintain vehicle speed at a selectedspeed when the vehicle is travelling at speeds in excess of 25 kph. Thecruise control system 16 is provided with a cruise control HMI (humanmachine interface) 18 by which means the user can input a target vehiclespeed to the cruise control system 16 in a known manner. In oneembodiment of the invention, cruise control system input controls aremounted to a steering wheel 171 (FIG. 5). The cruise control system 16may be switched on by pressing a cruise control system selector button176. When the cruise control system 16 is switched on, depression of a‘set-speed’ control 173 sets the current value of a cruise controlset-speed parameter, cruise_set-speed to the current vehicle speed.Depression of a ‘+’ button 174 allows the value of cruise_set-speed tobe increased whilst depression of a ‘−’ button 175 allows the value ofcruise_set-speed to be decreased. A resume button 173R is provided thatis operable to control the cruise control system 16 to resume speedcontrol at the instant value of cruise_set-speed following driverover-ride. It is to be understood that known on-highway cruise controlsystems including the present system 16 are configured so that, in theevent that the user depresses the brake or, in the case of vehicles witha manual transmission, a clutch pedal, the cruise control function iscancelled and the vehicle 100 reverts to a manual mode of operationwhich requires accelerator pedal input by a user in order to maintainvehicle speed. In addition, detection of a wheel slip event, as may beinitiated by a loss of traction, also has the effect of cancelling thecruise control function. Speed control by the system 16 is resumed ifthe driver subsequently depresses the resume button 173R.

The cruise control system 16 monitors vehicle speed and any deviationfrom the target vehicle speed is adjusted automatically so that thevehicle speed is maintained at a substantially constant value, typicallyin excess of 25 kph. In other words, the cruise control system isineffective at speeds lower than 25 kph. The cruise control HMI 18 mayalso be configured to provide an alert to the user about the status ofthe cruise control system 16 via a visual display of the HMI 18. In thepresent embodiment the cruise control system 16 is configured to allowthe value of cruise_set-speed to be set to any value in the range 25-150kph.

The LSP control system 12 also provides a speed-based control system forthe user which enables the user to select a very low target speed atwhich the vehicle can progress without any pedal inputs being requiredby the user. Low-speed speed control (or progress control) functionalityis not provided by the on-highway cruise control system 16 whichoperates only at speeds above 25 kph.

The LSP control system 12 is activated by means of a LSP control systemselector button 172 mounted on the steering wheel 171. The system 12 isoperable to apply selective powertrain, traction control and brakingactions to one or more wheels of the vehicle 100, collectively orindividually, to maintain the vehicle 100 at the desired speed.

The LSP control system 12 is configured to allow a user to input adesired value of set-speed parameter, LSP_set-speed (alternativelyreferred to herein as target set-speed) to the LSP control system 12 viaa low-speed progress control HMI (LSP HMI) 20 (FIG. 1, FIG. 3) whichshares certain input buttons 173-175 with the cruise control system 16and HDC control system 12HD. Provided the vehicle speed is within theallowable range of operation of the LSP control system (which is therange from 2 to 30 kph in the present embodiment although other rangesare also useful) the LSP control system 12 controls vehicle speed inaccordance with the value of LSP_set-speed. Unlike the cruise controlsystem 16, the LSP control system 12 is configured to operateindependently of the occurrence of a traction event. That is, the LSPcontrol system 12 does not cancel speed control upon detection of wheelslip. Rather, the LSP control system 12 actively manages vehiclebehavior when slip is detected.

The LSP control HMI 20 is provided in the vehicle cabin so as to bereadily accessible to the user. The user of the vehicle 100 is able toinput to the LSP control system 12, via the LSP HMI 20, an indication ofthe speed at which the user desires the vehicle to travel (referred toas “the target speed”) by means of the ‘set-speed’ button 173 and the 47‘+’/‘−’ buttons 174, 175 in a similar manner to the cruise controlsystem 16. The LSP HMI 20 also includes a visual display upon whichinformation and guidance can be provided to the user about the status ofthe LSP control system 12.

The LSP control system 12 receives an input from the braking system 22of the vehicle indicative of the extent to which the user has appliedbraking by means of the brake pedal 163. The LSP control system 12 alsoreceives an input from an accelerator pedal 161 indicative of the extentto which the user has depressed the accelerator pedal 161. An input isalso provided to the LSP control system 12 from the transmission orgearbox 124. This input may include signals representative of, forexample, the speed of an output shaft of the gearbox 124, torqueconverter slip and a gear ratio request. Other inputs to the LSP controlsystem 12 include an input from the cruise control HMI 18 which isrepresentative of the status (ON/OFF) of the cruise control system 16,and an input from the LSP control HMI 20.

The HDC function block of the VCU 10 forms part of a HDC system 12HD.When the HDC system 12HD is active, the system 12HD controls the brakingsystem 22 (of which the ABS function block forms part) in order to limitvehicle speed to a value corresponding to that of a HDC set-speedparameter HDC_set-speed which may be set by a user. The HDC set-speedmay also be referred to as an HDC target speed. Provided the user doesnot override the HDC system by depressing the accelerator pedal when theHDC system is active, the HDC system 12HD controls the braking system 22(FIG. 3) to prevent vehicle speed from exceeding the HDC_set-speed. Inthe present embodiment the HDC system 12HD is not operable to applypositive drive torque. Rather, the HDC system 12HD is only operable toapply negative brake torque.

A HDC system HMI 20HD is provided by means of which a user may controlthe HDC system 12HD, including setting the value of HDC_set-speed. AnHDC system selector button 177 is provided on the steering wheel 171 bymeans of which a user may activate the HDC system 12HD to controlvehicle speed.

As noted above, the HDC system 12HD is operable to allow a user to set avalue of HDC set-speed parameter HDC_set-speed and to adjust the valueof HDC_set-speed using the same controls as the cruise control system 16and LSP control system 12. Thus, in the present embodiment, when the HDCsystem 12HD is controlling vehicle speed, the HDC system set-speed maybe increased, decreased or set to an instant speed of the vehicle in asimilar manner to the set-speed of the cruise control system 16 and LSPcontrol system, using the same control buttons 173, 173R, 174, 175. TheHDC system 12HD is operable to allow the value of HDC_set-speed to beset to any value in the range from 2-30 kph.

If the HDC system 12HD is selected when the vehicle 100 is travelling ata speed of 50 kph or less and no other speed control system is inoperation, the HDC system 12HD sets the value of HDC_set-speed to avalue selected from a look-up table. The value output by the look-uptable is determined in dependence on the identity of the currentlyselected transmission gear, the currently selected PTU gear ratio(Hi/LO) and the currently selected driving mode. The HDC system 12HDthen applies the powertrain 129 and/or braking system 22 to slow thevehicle 100 to the HDC system set-speed provided the driver does notoverride the HDC system 12HD by depressing the accelerator pedal 161.The HDC system 12HD is configured to slow the vehicle 100 to theset-speed value at a deceleration rate not exceeding a maximum allowablerate. The rate is set as 1.25 ms-2 in the present embodiment, howeverother values are also useful. If the user subsequently presses the‘set-speed’ button 173 the HDC system 12HD sets the value ofHDC_set-speed to the instant vehicle speed provided the instant speed is30 kph or less. If the HDC system 12HD is selected when the vehicle 100is travelling at a speed exceeding 50 kph, the HDC system 12HD ignoresthe request and provides an indication to the user that the request hasbeen ignored.

It is to be understood that the VCU 10 is configured to implement aknown Terrain Response® (TR) system of the kind described above in whichthe VCU 10 controls settings of one or more vehicle systems orsub-systems such as the powertrain controller 11 in dependence on aselected driving mode. The driving mode may be selected by a user bymeans of a driving mode selector 141S (FIG. 1). The driving modes mayalso be referred to as terrain modes, terrain response modes, or controlmodes. In the embodiment of FIG. 1 four driving modes are provided: an‘on-highway’ driving mode suitable for driving on a relatively hard,smooth driving surface where a relatively high surface coefficient offriction exists between the driving surface and wheels of the vehicle; a‘sand’ driving mode suitable for driving over sandy terrain; a ‘grass,gravel or snow’ driving mode suitable for driving over grass, gravel orsnow, a ‘rock crawl’ driving mode suitable for driving slowly over arocky surface; and a ‘mud and ruts’ driving mode suitable for driving inmuddy, rutted terrain. Other driving modes may be provided in additionor instead.

In some embodiments, the LSP control system 12 may be in either one ofan active condition, a standby condition and an ‘off’ condition. In theactive condition, the LSP control system 12 actively manages vehiclespeed by controlling powertrain torque and braking system torque. In thestandby condition, the LSP control system 12 does not control vehiclespeed until a user presses the resume button 173R or the ‘set speed’button 173. In the off condition the LSP control system 12 is notresponsive to input controls until the LSP control system selectorbutton 172 is depressed.

In the present embodiment the LSP control system 12 is also operable toassume an intermediate condition similar to that of the active mode butin which the LSP control system 12 is prevented from commanding theapplication of positive drive torque to one or more wheels of thevehicle 100 by the powertrain 129. Thus, only braking torque may beapplied, by means of the braking system 22 and/or powertrain 129. Otherarrangements are also useful.

With the LSP control system 12 in the active condition, the user mayincrease or decrease the vehicle set-speed by means of the ‘+’ and ‘−’buttons 174, 175. In addition, the user may optionally also increase ordecrease the vehicle set-speed by lightly pressing the accelerator orbrake pedals 161, 163 respectively. In some embodiments, with the LSPcontrol system 12 in the active condition the ‘+’ and ‘−’ buttons 174,175 may be disabled such that adjustment of the value of LSP_set-speedcan only be made by means of the accelerator and brake pedals 161, 163.This latter feature may prevent unintentional changes in set-speed fromoccurring, for example due to accidental pressing of one of the ‘+’ or‘−’ buttons 174, 175. Accidental pressing may occur for example whennegotiating difficult terrain where relatively large and frequentchanges in steering angle may be required. Other arrangements are alsouseful.

It is to be understood that in the present embodiment the LSP controlsystem 12 is operable to cause the vehicle to travel in accordance witha value of set-speed in the range from 2-30 kph whilst the cruisecontrol system is operable to cause the vehicle to travel in accordancewith a value of set-speed in the range from 25-150 kph although othervalues are also useful. If the LSP control system 12 is selected whenthe vehicle speed is above 30 kph but less than or substantially equalto 50 kph, the LSP control system 12 assumes the intermediate mode. Inthe intermediate mode, if the driver releases the accelerator pedal 161whilst travelling above 30 kph the LSP control system 12 deploys thebraking system 22 to slow the vehicle 100 to a value of set-speedcorresponding to the value of parameter LSP_set-speed. Once the vehiclespeed falls to 30 kph or below, the LSP control system 12 assumes theactive condition in which it is operable to apply positive drive torquevia the powertrain 129, as well as brake torque via the powertrain 129(via engine braking) and the braking system 22 in order to control thevehicle in accordance with the LSP_set-speed value. If no LSP set-speedvalue has been set, the LSP control system 12 assumes the standby mode.

It is to be understood that if the LSP control system 12 is in theactive mode, operation of the cruise control system 16 is inhibited. Thetwo systems 12, 16 therefore operate independently of one another, sothat only one can be operable at any one time, depending on the speed atwhich the vehicle is travelling.

In some embodiments, the cruise control HMI 18 and the LSP control HMI20 may be configured within the same hardware so that, for example, thespeed selection is input via the same hardware, with one or moreseparate switches being provided to switch between the LSP input and thecruise control input.

FIG. 4 illustrates the means by which vehicle speed is controlled in theLSP control system 12. As described above, a speed selected by a user(set-speed) is input to the LSP control system 12 via the LSP controlHMI 20. A vehicle speed sensor 34 associated with the powertrain 129(shown in FIG. 1) provides a signal 36 indicative of vehicle speed tothe LSP control system 12. The LSP control system 12 includes acomparator 28 which compares the set-speed 38 (also referred to as a‘target speed’ 38) selected by the user with the measured speed 36 andprovides an output signal 30 indicative of the comparison. The outputsignal 30 is provided to an evaluator unit 40 of the VCU 10 whichinterprets the output signal 30 as either a demand for additional torqueto be applied to the vehicle wheels 111-115, or for a reduction intorque applied to the vehicle wheels 111-115, depending on whether thevehicle speed needs to be increased or decreased to maintain the speedLSP_set-speed. An increase in torque is generally accomplished byincreasing the amount of powertrain torque delivered to a given positionof the powertrain, for example an engine output shaft, a wheel or anyother suitable location. A decrease in torque at a given wheel to avalue that is less positive or more negative may be accomplished bydecreasing powertrain torque delivered to a wheel and/or by increasing abraking force on a wheel. It is to be understood that in someembodiments in which a powertrain 129 has one or more electric machinesoperable as a generator, negative torque may be applied by thepowertrain 129 to one or more wheels by the electric machine. Negativetorque may also be applied by means of engine braking in somecircumstances, depending at least in part on the speed at which thevehicle 100 is moving. If one or more electric machines are providedthat are operable as propulsion motors, positive drive torque may beapplied by means of the one or more electric machines.

An output 42 from the evaluator unit 40 is provided to the powertraincontroller 11 and brake controller 13 which in turn control a net torqueapplied to the vehicle wheels 111-115. The net torque may be increasedor decreased depending on whether the evaluator unit 40 demands positiveor negative torque. In order to cause application of the necessarypositive or negative torque to the wheels, the evaluator unit 40 maycommand that positive or negative torque is applied to the vehiclewheels by the powertrain 129 and/or that a braking force is applied tothe vehicle wheels by the braking system 22, either or both of which maybe used to implement the change in torque that is necessary to attainand maintain a required vehicle speed. In the illustrated embodiment thetorque is applied to the vehicle wheels individually so as to maintainthe vehicle at the required speed, but in another embodiment torque maybe applied to the wheels collectively to maintain the required speed. Insome embodiments, the powertrain controller 11 may be operable tocontrol an amount of torque applied to one or more wheels by controllinga driveline component such as a rear drive unit, front drive unit,differential or any other suitable component. For example, one or morecomponents of the driveline 130 may include one or more clutchesoperable to allow an amount of torque applied to one or more wheels tobe varied. Other arrangements are also useful.

Where a powertrain 129 includes one or more electric machines, forexample one or more propulsion motors and/or generators, the powertraincontroller 11 may be operable to modulate torque applied to one or morewheels by means of one or more electric machines.

The LSP control system 12 also receives a signal 48 indicative of awheel slip event having occurred. This may be the same signal 48 that issupplied to the on-highway cruise control system 16 of the vehicle, andwhich in the case of the latter triggers an override or inhibit mode ofoperation in the on-highway cruise control system 16 so that automaticcontrol of vehicle speed by the on-highway cruise control system 16 issuspended or cancelled. However, the LSP control system 12 is notarranged to cancel or suspend operation in dependence on receipt of awheel slip signal 48 indicative of wheel slip. Rather, the system 12 isarranged to monitor and subsequently manage wheel slip so as to reducedriver workload. During a slip event, the LSP control system 12continues to compare the measured vehicle speed with the value ofLSP_set-speed, and continues to control automatically the torque appliedto the vehicle wheels so as to maintain vehicle speed at the selectedvalue. It is to be understood therefore that the LSP control system 12is configured differently to the cruise control system 16, for which awheel slip event has the effect of overriding the cruise controlfunction so that manual operation of the vehicle must be resumed, orspeed control by the cruise control system 12 resumed by pressing theresume button 173R or set-speed button 173.

In a further embodiment of the present invention (not shown) a wheelslip signal 48 is derived not just from a comparison of wheel speeds,but further refined using sensor data indicative of the vehicle's speedover ground. Such a speed over ground determination may be made viaglobal positioning (GPS) data, or via a vehicle mounted radar or laserbased system arranged to determine the relative movement of the vehicle100 and the ground over which it is travelling. A camera system may beemployed for determining speed over ground in some embodiments.

At any stage of the LSP control process the user can override thefunction by depressing the accelerator pedal 161 and/or brake pedal 163to adjust the vehicle speed in a positive or negative sense. However, inthe event that a wheel slip event is detected via signal 48, the LSPcontrol system 12 remains active and control of vehicle speed by the LSPcontrol system 12 is not suspended. As shown in FIG. 4, this may beimplemented by providing a wheel slip event signal 48 to the LSP controlsystem 12 which is then managed by the LSP control system 12. In theembodiment shown in FIG. 1 the SCS 14 generates the wheel slip eventsignal 48 and supplies it to the LSP control system 12 and cruisecontrol system 16.

A wheel slip event is triggered when a loss of traction occurs at anyone of the vehicle wheels. Wheels and tires may be more prone to losingtraction when travelling for example on snow, ice, mud or sand and/or onsteep gradients or cross-slopes. A vehicle 100 may also be more prone tolosing traction in environments where the terrain is more uneven orslippery compared with driving on a highway in normal on-roadconditions. Embodiments of the present invention therefore findparticular benefit when the vehicle 100 is being driven in an off-roadenvironment, or in conditions in which wheel slip may commonly occur.Manual operation in such conditions can be a difficult and oftenstressful experience for the driver and may result in an uncomfortableride.

The vehicle 100 is also provided with additional sensors (not shown)which are representative of a variety of different parameters associatedwith vehicle motion and status. These may be inertial systems unique tothe LSP or HDC control system 12, 12HD or part of an occupant restraintsystem or any other sub-system which may provide data from sensors suchas gyros and/or accelerometers that may be indicative of vehicle bodymovement and may provide a useful input to the LSP and/or HDC controlsystems 12, 12HD. The signals from the sensors provide, or are used tocalculate, a plurality of driving condition indicators (also referred toas terrain indicators) which are indicative of the nature of the terrainconditions over which the vehicle is travelling.

The sensors (not shown) on the vehicle 100 include, but are not limitedto, sensors which provide continuous sensor outputs to the VCU 10, asmentioned previously and as shown in FIG. 3, an ambient temperaturesensor, an atmospheric pressure sensor, tyre pressure sensors, wheelarticulation sensors, gyroscopic sensors to detect vehicular yaw, rolland pitch angle and rate, a vehicle speed sensor, a longitudinalacceleration sensor, an engine torque sensor (or engine torqueestimator), a steering angle sensor, a steering wheel speed sensor, agradient sensor (or gradient estimator), a lateral acceleration sensorwhich may be part of the SCS 14, a brake pedal position sensor, a brakepressure sensor, an accelerator pedal position sensor, longitudinal,lateral and vertical motion sensors, and water detection sensors formingpart of a vehicle wading assistance system (not shown). In otherembodiments, only a selection of the aforementioned sensors may be used.

The front wheels 111, 112 in combination with the front drive shafts 118and front differential 137 may be referred to as a front axle 136F. Therear wheels 114, 115 in combination with rear drive shafts 139 and reardifferential 135 may be referred to as a rear axle 136R.

The wheels 111, 112, 114, 115 each have a respective brake 111B, 112B,114B, 115B. Respective speed sensors 111S, 112S, 114S, 115S areassociated with each wheel 111, 112, 114, 115 of the vehicle 100. Thesensors 111S, 112S, 114S, 115S are mounted to a chassis 100C of thevehicle 100 and arranged to measure a speed of the corresponding wheel.

The VCU 10 also receives a signal from the steering controller 170C. Thesteering controller 170C is in the form of an electronic power assistedsteering unit (ePAS unit). The steering controller 170C provides asignal to the VCU 10 indicative of the steering force being applied tosteerable road wheels 111, 112 of the vehicle 100. This forcecorresponds to that applied by a user to the steering wheel 171 incombination with steering force generated by the ePAS unit 170C.

The VCU 10 evaluates the various sensor inputs to determine theprobability that each of a plurality of different control modes (drivingmodes) for the vehicle subsystems is appropriate, with each control modecorresponding to a particular terrain type over which the vehicle istravelling (for example, mud and ruts, sand, grass/gravel/snow).

If the user has selected operation of the vehicle in an automaticdriving mode selection condition, the VCU 10 then selects the mostappropriate one of the control modes and is configured automatically tocontrol the subsystems according to the selected mode. This aspect ofthe illustrated embodiment is described in further detail in ourco-pending patent application nos. GB1111288.5, GB1211910.3 andGB1202427.9, the contents of each of which is incorporated herein byreference.

The nature of the terrain over which the vehicle is travelling (asdetermined by reference to the selected control mode) may also beutilized in the LSP control system 12 to determine an appropriateincrease or decrease in vehicle speed. For example, if the user selectsa value of LSP_set-speed that is not suitable for the nature of theterrain over which the vehicle is travelling, the system 12 is operableto automatically adjust the vehicle speed downwards by reducing thespeed of the vehicle wheels. In some cases, for example, the userselected speed may not be achievable or appropriate over certain terraintypes, particularly in the case of uneven or rough surfaces. If thesystem 12 selects a set-speed that differs from the user-selectedset-speed, a visual indication of the speed constraint is provided tothe user via the LSP HMI 20 to indicate that an alternative speed hasbeen adopted.

B-722: ATPC-Set-Speed Adjustment Management at Low Speed whenEncountering of an Obstacle

In the system described above when a vehicle encounters an object orobstacle such as a boulder, curb, or log, especially when travelling atvery low speeds, it may temporarily stop as the torque previously beingdelivered to the wheels is insufficient to drive the vehicle over theobstacle and there is a slight time lag as the torque is increased.Alternatively the driver may manually slow and stop the vehicle as itencounters the object prior to driving the vehicle over the object. In ascenario where the vehicle is stopped, or substantially at a stand-stillwith the leading wheels adjacent an obstruction, if the driver increasesthe LSP_set-speed, for example if he believes that the vehicle needs ahigher set-speed to overcome the object, or pressed the LSP resumebutton to re-engage LSP control at the previously saved LSP_set-speed,then once the vehicle crests the object it will accelerate aggressivelyup to the selected LSP_set-speed due to an artificially andunintentionally high disparity between the instantaneous speed onovercoming the obstacle and the user increased or resumed LSP_set-speed.As the torque at the point of cresting the object will be high, and asthere is a large disparity between the current vehicle speed and theLSP_set-speed then the vehicle may surge forwards at a speed in a mannernot intended by the driver. This may be detrimental to vehiclecomposure.

To overcome this problem, the control system of the vehicle controls thespeed of the vehicle to a vehicle control speed in dependence uponLSP_set-speed and it will be appreciated that in many driving conditionsthe vehicle control speed will be the LSP_set-speed. However, thevehicle control speed may vary from the LSP_set-speed, in particular thevehicle control speed may be reduced if the vehicle is travelling at avery low speed or is starting from rest. Furthermore the torque requestsignal may be used as an input upon which the reduction in the vehiclecontrol speed is calculated. In this manner the speed to which thevehicle is controlled is reduced when the vehicle is substantially at astandstill and a high torque is being requested. In this manner, whenthe obstacle resulting in the high torque request is overcome there willbe only a small difference between the vehicle speed and the vehiclecontrol speed and the result will be a rapid reduction in the positivetorque being delivered to the wheels, thereby allowing the vehicle tomove forward in a more composed manner with vehicle acceleration beingcontrolled in dependence on a detected obstacle. Effectively thereforean at least temporary cap is applied to the acceleration.

In an embodiment the LSP_set-speed may be maintained and once theobstacle is overcome and the torque is reduced, the vehicle controlspeed may automatically increase back up to the LSP_set-speed along aprescribed acceleration profile, however as the vehicle control speed isa function of the torque this will only occur once the torque has beenreduced and thereby prevent any sudden or forceful vehicle motion as itnegotiates and overcomes the obstruction. The control system may alsohave a delay prior to increasing the vehicle control speed back towardsthe LSP_set-speed. This is particularly beneficial as if the leadingwheels have passed over the object it is likely that the trailing wheelswill also encounter the same object and accordingly it may be beneficialto maintain a reduced vehicle control speed until the rear wheels havealso overcome the obstacle. Further, the delay will give the driver timeto assess the terrain in front of the obstacle.

In another embodiment the system may actually reduce the LSP_set-speed,and only allow the vehicle to resume progress at a higher speed inresponse to a user input to increase the LSP_set-speed. TheLSP_set-speed may be reduced to the vehicle control speed oralternatively the LSP_set-speed may be reduced to a value below itsprevious value but above the vehicle control speed by a value of ΔV_set_max, such that:reduced LSP_set-speed=vehicle control speed+ΔV_set_max,where Δ V_set_max defines a maximum value by which the target set-speed(LSP_set-speed) is allowed to exceed the vehicle control speed for agiven instantaneous vehicle speed. In this manner, after cresting anobject, the vehicle will progress at the reduced vehicle control speedto which the LSP_set-speed has been temporarily adjusted until thedriver takes positive action to increase the speed.

As when the vehicle is at a stand-still or is a virtual stand-still,i.e. it is only travelling very slowly, it may be advantageous to limitthe amount by which the driver can increase the LSP_set-speed so as toat least in part mitigate the problem of large discrepancies betweenactual vehicle speed and LSP_set-speed, in particular when large torquesare being, or will be, applied to the wheels. Accordingly, in a controlsystem of an embodiment of the invention, changes to the LSP_set-speedmay be limited in dependence upon, or as a function of, theinstantaneous vehicle speed. In particular, a controller of the systemmay also limit the maximum input LSP_set-speed in dependence upon theterrain over which the vehicle is travelling. Limiting the maximum inputtarget set-speed may be effected by the system defining a maximum ΔV_set in dependence upon the instantaneous vehicle speed, where Δ V_setis the difference between an existing target set-speed, and a new userinput target set-speed. The system will therefore not allow the user toinput a LSP_set-speed that would result in Δ V_set exceeding the maximumΔ V_set.

Operation of a control system function according to an embodiment of theinvention will now be described by reference to flow diagram FIG. 6.

At step S101 the control system verifies if the LSP control system is inan active configuration. If the control system determines that the LSPcontrol system is in an active configuration then the method continuesto step S103.

At step S103 the control system determines the actual vehicle speed, forexample by reference to wheel speed sensors, GPS data or the like, anddetermines if the vehicle speed is below the LSP_control_speed. If thevehicle speed is not below the LSP_control_speed the method progressesto step S115 as described below. If the vehicle speed is below theLSP_control_speed the method progresses to step S105.

At step S105 the control system determines if the torque request signalis high for the vehicle speed (and/or for the difference between theactual vehicle speed and the LSP_set-speed). If the torque requestsignal is not high for the vehicle speed then this is indicative of thevehicle is not currently trying to overcome an obstruction and is merelyattempting to reach its LSP_set-speed, and the method progresses to stepS113 which is described in more detail below.

If the torque request signal is high for the vehicle speed (and/or forthe difference between the actual vehicle speed and the LSP_set-speed)then that can be taken as indicative of the vehicle attempting totraverse or overcome an obstacle that requires substantially more drivetorque than driving across a substantially flat terrain, and the methodprogresses to step S106.

At step S106 the system determines if the vehicle control speed is abovea speed and/or torque dependant target vehicle control speed. If thesystem determines that the vehicle control speed is not above a speedand/or torque dependant target vehicle control speed then the methodprogresses to step S109. If the system determines that the vehiclecontrol speed is above a speed and/or torque dependant target vehiclecontrol speed then the method progresses to step S107.

At step S107 wherein the vehicle control speed is reduced. Optionallythe method may, at this time, include step S111 wherein theLSP_set-speed is also reduced. The vehicle control speed is reduced to avalue that is dependent upon the amount of torque being requested. Themethod then progresses to step S109.

At step S109 the control system controls the vehicle to the vehiclecontrol speed and then loops back to step S101, and the control loopcontinues.

If at Step 105 the torque is not high for the given speed, then themethod progresses to step S113 as stated above. At step S113 the systemdetermines if the vehicle control speed is below the LSP_set-speed. Ifso, this is indicative that the vehicle control speed had been reducedin a previous loop of the method, i.e. the vehicle encountered anobstacle and has now negotiated the obstacle. If the system determinesthat the vehicle control speed is below the LSP_set-speed then a timedelay is introduced prior to the method progressing to step S115. In oneembodiment the time delay may take into consideration the wheelbase ofthe vehicle and the vehicle speed to ensure that the time delay issufficient that if a trailing wheel of the vehicle will also traversethe same obstacle then the vehicle does not accelerate until all wheelshave cleared the obstacle. Other time delays may be useful. At stepS113, if the system determines that the vehicle control speed is notbelow the LSP_set-speed then this is indicative of the vehicleaccelerating to a LSP_set-speed under normal conditions and the methodprogresses directly to step S115 without the time delay.

At step S115 the control system controls the vehicle to obtain andmaintain the LSP_set-speed.

B-722 Terrain Type and Speed Adaptation for ATPC Torque Control toEnhance Composure

When a driver cannot see, via the vehicle HMI interface, theLSP_set-speed that they set using the cruise control buttons 174, 175 itis possible for them to press and hold the “set +” button and set atarget speed that is much higher than the current vehicle speed. Thismay be because the actual speed is not displayed or because the driveris concentrating on controlling the direction of the vehicle and is notlooking at the vehicle display.

This can result in the vehicle accelerating to the target speed whichmay be set unintentionally high, which may feel disconcerting to thedriver as they do not know when the vehicle is going to stopaccelerating.

As the set + button is pressed the vehicle speed is incrementallyincreased in a time dependent manner, for example 1 mph for every secondthe button is pressed. Where the vehicle accelerates at a slower ratethan the LSP_set-speed is increasing a disparity may occur between thecurrent vehicle speed and the LSP_set-speed when the driver releases theset + button, and the vehicle may then continue to accelerate in amanner unexpected, or more than anticipated by the driver. This can bemitigated in part by operating the vehicle speed such that the vehicleaccelerates while the + button is being depressed and the system thenlimits any additional speed increase after the set + button is releasedto a fixed value, irrespective of the value the LSP_set-speed shouldhave risen to based purely on the amount of time the set + button waspressed for. This prevents the vehicle accelerating faster than intendedonce the button is released due to an unintentionally high set speed. Inparticular this may occur when driving off road in variable conditionsas the vehicle may be limited in its rate of acceleration by suchfactors slip events occurring at vehicle wheels. In such circumstancesthere is an increased likelihood that the driver will be concentratingon controlling the trajectory of the vehicle rather than watching thevehicle HMI interface which may be displaying the set speed. Thelimiting of any additional acceleration therefore binds the target speed(LSP_set-speed) to the vehicle speed so the vehicle behavior on a pressand hold of the + button feels like the driver is accelerating the carwhilst holding the button. On release the car accelerates the last,limited, amount to the target.

However, during low speed driving this method of using a cappedadditional speed increase when the set + button is released can stillinadvertently cause loss of composure as the last part of accelerationmay be result in a LSP_set-speed that is too great for the terrain type,especially on rough surfaces. The driver may therefore inadvertentlypress and hold the set + button causing the vehicle to accelerate to aspeed that is uncomfortably fast for the surface.

In order to overcome this, a vehicle speed control system may beconfigured to automatically control the speed of the vehicle to avehicle control speed by way of the LSP_set-speed which is controlled asa function of at least one of the instantaneous vehicle speed and theterrain over which the vehicle is travelling.

In one arrangement the vehicle comprises a TR controller via which theterrain mode can be set by the driver. The vehicle speed control systemcan control the vehicle control speed, in dependence upon theLSP_set-speed, as a function of the terrain over which the vehicle istravelling in dependence on a signal indicative a user selected terrainmode. Alternatively the vehicle may have an automatic terrain response(TR) controller as described herein above and the system may control thevehicle control speed, in dependence upon the LSP_set-speed, as afunction of the terrain over which the vehicle is travelling independence on a signal indicative a terrain mode automatically selectedin dependence on sensed vehicle and/or environmental parameters.

The vehicle may be controlled as described above wherein the vehicleaccelerates as the driver holds the set + button and when the driverreleases the set + button. If the LSP_set-speed is greater than thecurrent vehicle speed controller may set the LSP_set-speed the currentvehicle speed plus a maximum allowable additional amount wherein saidmaximum additional amount is a function the instantaneous vehicle speedand the terrain over which the vehicle is travelling.

The system may cap the maximum LSP_set-speed to which the set + buttonwill set the LSP_set-speed, and therefore to which the control systemwill accelerate the vehicle, in dependence upon the at least one of theinstantaneous vehicle speed and the terrain over which the vehicle istravelling. In this way the driver cannot inadvertently request thevehicle accelerate and be controlled to a LSP_set-speed that is greaterthan that appropriate for the terrain which is being traversed. Themaximum LSP_set-speed (LSP_set-speed_max) may be defined as an absoluteamount in dependence on the at least one of the instantaneous vehiclespeed and the terrain over which the vehicle is travelling.Alternatively the system may limit the maximum input target set-speed bydefining a maximum Δ V_set based on the at least one of theinstantaneous vehicle speed and the terrain over which the vehicle istravelling, where Δ V_set is the difference between an existing targetset-speed, and a new user input target set-speed; i.e., the system doesnot allow more than a specified addition to the current LSP_set-speed tobe requested and that difference is dependent upon the at least one ofthe instantaneous vehicle speed and the terrain over which the vehicleis travelling.

Operation of a control system function according to an embodiment of theinvention will now be described by reference to flow diagram FIG. 7.

At step S201 the control system verifies if the LSP control system is inan active configuration. If the control system determines that the LSPcontrol system is in an active configuration then the method continuesto step S203.

At step S203 the system determines if the driver is pressing the Set +button. If the set + button is not being pressed the method loops backto step S201. If the set + button is being pressed the method continuesto step S205.

At step S205 the system determines of the LSP_set-speed is already atthe maximum allowable set-speed LSP_set-speed_max. To perform thisfunctionality the controller acquires data relating one or both of theinstantaneous vehicle speed and the terrain type over which the vehicleis traversing. The Terrain type is obtained by the TR controller and maybe a user input TR mode, or may be an automatically determined TR mode.The controller then looks up a value of LSP_set-speed_max, correlatingto the identified instantaneous vehicle speed and/or terrain type, in alook-up table in a memory of the system. If the LSP_set-speed is equalto the LSP_set-speed_max for the prevailing conditions then no furtherincrease to the LSP_set-speed and no acceleration are permitted. Themethod then continues to step S215 wherein the system controls the speedof the vehicle to the LSP_set-speed. If the LSP_set-speed is below theLSP-set_speed_max then the system continues to step S207 wherein thevehicle incrementally accelerates and the LSP_set-speed is increased tomatch the increased vehicle speed. The method then continues to stepS209.

At step S209 the system determines if the set + button has been releasedor if it continues to remain pressed. If the set + button remainspressed the method loops back to step S205. In this manner, while theset + button remains pressed the control system will increase the torqueat the wheels to accelerate the vehicle. The rate of acceleration may bea predetermined rate and may for example be dependent upon factors suchas the TR mode in which the vehicle is operating, and other factors suchas vehicle attitude and detected slip events. Other factors indetermining appropriate acceleration may be useful. The rate at whichthe torque is increased (i.e. the vehicle acceleration) may varydepending on one or both of the instantaneous speed and the TR mode inwhich the vehicle is operating. This loop will continue until either theLSP_set-speed_max is reached, or until at step S209 the systemdetermines that the set + button has been released. If at step S209 thesystem determines that the set + button has been released the methodcontinues to step S211.

At step S211 a further check is made as to whether the LSP_set-speed_maxhas been reached. If so the method progressed to step S215 and thesystem controls the vehicle to the LSP_set-speed. If however theLSP_set-speed_max has not been reached then the method continues to stepS213.

At step S213, upon release of the set + button the vehicle will assignthe LSP_set-speed a value equal to the lower of LSP_set-speed andLSP_set-speed_max, wherein LSP_set-speed_max is defined by currentvehicle speed+ Δ V_set_max, where Δ V_set_max defines a maximum value bywhich the LSP_set-speed is allowed to exceed the instantaneous vehiclespeed for the prevailing terrain type; i.e. if the LSP_set-speed ishigher than the current vehicle speed when the set + button is releasedthe vehicle will continue to accelerate towards the LSP_set-speed, themagnitude of the continued acceleration being determined in dependenceon the speed of the vehicle and/or the prevailing TR mode. The value ofΔ V_set_max is obtained by the system from look up tables stored in amemory of the control system. The method then continues to step S215wherein the vehicle is controlled to the LSP_set-speed.

Although described herein in relation to a set + button it will berecognized that when LSP control mode is operational the accelerator maybe configured to act as the set + button and the above method and systemmay substitute activation of the set + button with the accelerator beingpressed when the vehicle is operating in LSP control mode.

B724-ATPC Variable Set Speed Incremental Adjustment Based on PrevailingTerrain Type.

It has been recognized that where a vehicle is used for traversingvaried terrain, the vehicle response to same command input given to thevehicle may result in a different behavior in dependence upon theprevailing terrain. In particular due to, for example, the differentdrag imposed on the vehicle by different surfaces, and the differentsurface frictions, as the vehicle accelerates, by application of anincreased positive torque to the driving wheels, and decelerates by areduction in positive torque or an application of negative torque to thedriving wheels, the response of the vehicle may be different dependingon the terrain type. Furthermore, for different terrain types differentlevels of driver control will be needed due to the nature of theterrain. For example, when driving on a hard flat surface such as tarmacor concrete driver workload is relatively low, whereas when crossing aboulder field strewn with rocks of different sizes, the driver workloadwould be relatively high. For these reasons, at least, it may bedesirable for the vehicle to respond differently to the same driverinput in dependence upon the terrain type over which the vehicle istravelling so as to aid control of the vehicle, enhance composure, andreduce driver workload and fatigue when travelling off-road.

As described hereinabove, a low speed progress control system isproposed that controls the speed of the vehicle at speeds below thosecontrolled by standard cruise control systems and which is particularlysuited to off highway driving conditions.

The system controls the speed of the vehicle to a target set-speedLSP_set-speed that can be set and increased/decreased by, for example,the driver by pressing set + and set − buttons to incrementally increaseor decrease the set speed.

In this aspect of the disclosed embodiments, a vehicle speed controlsystem for a vehicle having a plurality of wheels is proposed, thevehicle speed control system is configured to automatically control thespeed of the vehicle in dependence on an input target set-speed. Thesystem comprises a means for receiving a user input of a targetset-speed at which the vehicle is intended to travel; a means forapplying torque to the at least one of the plurality of wheels forpropelling the vehicle at the vehicle control speed; and a means forcontrolling the target set-speed in dependence upon at least one if theinstantaneous vehicle speed and the terrain over which the vehicle istravelling.

The means for controlling the target set-speed comprises an input meansto enable the user to incrementally increase and/or decrease the targetset-speed upon each actuation of said input means by an incrementalvalue. The control system is configured to determine said incrementalvalue in dependence upon said at least one if the instantaneous vehiclespeed and terrain over which the vehicle is travelling.

The means for controlling the vehicle control speed in dependence uponthe terrain over which the vehicle is travelling comprises a set +button 174 and a set − button 175 disposed on the steering wheel 171 ofthe vehicle.

Each time the set + or the set − button is pressed the control systemincreases or decreases the LSP_set-speed by a predetermined amount. Inan alternative arrangement the set + or the set − button may increase ordecrease the amount of torque requested by the control system by apredetermined amount, resulting in an increase in the speed. TheLSP_set-speed may then be reset to the new vehicle speed.

The predetermined amount by which the set + and/or set − increase ordecrease the LSP_set-speed, or the torque request, are determined independence on the terrain over which the vehicle is travelling.

As described above the vehicle includes a TR controller that controlsthe vehicle set up in dependence upon the terrain over which the vehicleis travelling. The TR mode may be input by the user or may beautomatically determined and set by the TR controller in response todata gathered from a plurality of vehicle and/or environmental sensorsdisposed on the vehicle.

In one arrangement the control system may set the set + and set −increments in dependence upon a signal indicative of a user selectedterrain mode. Alternatively the control system may set the set + and/orset − increments in dependence upon a signal indicative a terrain modeautomatically selected in dependence on sensed vehicle and/orenvironmental parameters.

The control system includes a memory means which contains a look uptable correlating the + and/or − increment magnitudes to associated orappropriate TR modes. In one embodiment of this aspect of the inventionthe control system may verify in which TR mode the vehicle is operatingwhen the set + or set − button is selected and look up the appropriateincrement magnitude for that mode. Alternatively the setting orselection of the TR mode may automatically cause the control system tolook up the appropriate increment magnitude and store that for use uponactivation of the set + or set − buttons.

In particular the set + increments may be lower for more some TR modes,in particular those TR modes which may correlate to greater suspensiontravel or large torque changes. For example the TR modes may include a“Mud and Ruts” mode and a “Rock Crawl” mode and the set + increments maybe less for these modes than for other modes, e.g. sand; grass, gravel,snow; SPO etc. In this manner when activating the set + control theamount of acceleration may be reduced in some modes so that the vehicledoes not accelerate so much in response to a set + input, therebyallowing greater finesse of control in difficult terrain, resulting inimproved vehicle composure. Traction may also be improved as by reducingthe rate of change of LSP_set-speed the acceleration from current speedto the new LSP_set-speed will be reduced.

In some embodiments the set − control may be configured in the samemanner, however, alternatively the set − control may have a separatelook up table such that the set-controls can vary independently from theset + controls, or may be set to a constant value. It may, for example,be desirable for the deceleration increments to remain constant so whenslowing the vehicle the driver obtains the same or a similar slowing ofthe vehicle in all modes.

The magnitude of the increments maybe further amended in dependence uponthe instantaneous vehicle speed, in particular the increments may besmaller at lower speeds and greater at higher speeds. This may beachieved either by using look up tables correlating the TR modes andspeeds to increment values, or may be achieved by applying a function ofthe vehicle speed to the increment value. For example:Increment value=IV _(LOOKUP) ×C(V _(INST))wherein IV_(LOOKUP) is the IV value obtained from the look up table;V_(INST) is the instantaneous speed of the vehicle and C is a constant.

It is to be understood that in some embodiments an off road speedcontrol system may be operable in either forward or reverse driving use.

It is to be understood that the speed control system according to anembodiment of the present invention may form part of an ATPC(All-Terrain Progress Control) system, which may be arranged to workindependently or in conjunction with one or more vehicle control systemsarranged to optimize one or more vehicle configurations such as one ormore sub-system configurations for a given terrain over which thevehicle is travelling. An example of such a system is a TerrainResponse® system.

It will be understood that the embodiments described above are given byway of example only and are not intended to limit the invention, thescope of which is defined in the appended claims.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, means “including but not limited to”, andis not intended to (and does not) exclude other moieties, additives,components, integers or steps.

Throughout the description and claims of this specification, thesingular encompasses the plural unless the context otherwise requires.In particular, where the indefinite article is used, the specificationis to be understood as contemplating plurality as well as singularity,unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith.

The invention claimed is:
 1. A vehicle speed control system for avehicle having a plurality of wheels, the vehicle speed control systemconfigured to automatically control the speed of the vehicle to avehicle control speed in dependence on an input target set-speed andcomprising at least one electronic controller: said at least oneelectronic controller having an input for receiving an electrical signalindicative of a user input of a target set-speed at which the vehicle isintended to travel; said at least one electronic controller outputting asignal to apply torque to the at least one of the plurality of wheelsfor propelling the vehicle at the vehicle control speed; wherein said atleast one electronic controller is configured to control the vehiclecontrol speed as a function of at least the instantaneous vehicle speed,said at least one electronic controller having an evaluator unit forevaluating the torque to be applied to at least one of the vehiclewheels and outputting a torque request signal; and said at least oneelectronic controller is configured to reduce the vehicle control speedas a function of the torque request signal.
 2. The vehicle speed controlsystem as claimed in claim 1, wherein the at least one electroniccontroller is configured to: determine a current speed at which thevehicle is travelling; compare the current speed with the vehiclecontrol speed and provide an output indicative of the difference betweenthe current speed and the vehicle control speed; and evaluate the torqueto be applied to at least one of the vehicle wheels in dependence onsaid output indicative of the difference between the current speed andthe vehicle control speed, and output the torque request signal independence thereon.
 3. The vehicle speed control system according toclaim 1 wherein the at least one electronic controller is configured toreduce the vehicle control speed as a function of the torque requestsignal if the instantaneous vehicle speed is in the range of 0 to 3kilometers per hour.
 4. The vehicle speed control system as claimed inclaim 1, wherein the at least one electronic controller is configured tocontrol said vehicle control speed as a function of the terrain overwhich the vehicle is travelling in dependence on at least one of: asignal indicative a user selected terrain mode; a signal indicative aterrain mode automatically selected in dependence on sensed vehicleparameters; or a signal indicative a terrain mode automatically selectedin dependence on sensed environmental parameters.
 5. The vehicle speedcontrol system as claimed in claim 1 wherein automatically controllingthe speed of the vehicle to a vehicle control speed in dependence on aninput target set-speed further comprises: the at least one electroniccontroller limiting the maximum input target set-speed in dependenceupon said at least one of the instantaneous vehicle speed and theterrain over which the vehicle is travelling.
 6. The vehicle speedcontrol system as claimed in claim 5, wherein limiting the maximum inputtarget set-speed comprises: the system defining a maximum Δ V_set independence upon said at least one of the instantaneous vehicle speed andthe terrain over which the vehicle is travelling, where Δ V_set is thedifference between: one of an existing target set-speed or theinstantaneous speed of the vehicle; and a new user input targetset-speed.
 7. The vehicle speed control system according to claim 6wherein the maximum value of Δ V_set is reduced in dependence upon theinstantaneous torque being applied to the at least one of the pluralityof wheels.
 8. The vehicle speed control system according to claim 1wherein the at least one electronic controller is configured to reducethe target set-speed in dependence upon the vehicle control speed andwherein the target set-speed is reduced to vehicle control speed+ ΔV_set_max, wherein Δ V_set_max defines a maximum value by which thetarget set-speed is allowed to exceed the control speed at a givenvehicle speed.
 9. The vehicle speed control system according to claim 1wherein: the system comprises an input device for receiving a user inputof a target set-speed that enables the user to incrementally increasethe target set-speed by pressing and holding a target set-speed +button, and wherein the controller is configured to incrementallyincrease the target set-speed while the set-speed + button is held, and,once the set-speed + button is released the controller is configured tocontinue to increase the target set-speed by a value determined by thecontroller in dependence on at least one of the instantaneous vehiclespeed and the terrain over which the vehicle is travelling.
 10. Thevehicle speed control system according to claim 1, wherein: the systemcomprises an input device to enable the user to incrementally increaseand/or decrease the target set-speed upon each actuation of said inputdevice by an incremental value; and wherein the at least one electroniccontroller is configured to determine said incremental value independence upon at least one of: the instantaneous vehicle speed; thetarget set-speed; or the terrain over which the vehicle is travelling.11. The vehicle speed control system as claimed in claim 10, furthercomprising a terrain mode selection interface for receiving a user inputof the terrain over which the vehicle is travelling, and wherein saidincremental value is dependent upon a signal indicative of the terrainmode selected by the user.
 12. The vehicle speed control systemaccording to claim 11 wherein said control system is configured todetermine said incremental value further in dependence upon one of thespeed at which the vehicle is travelling and the target set-speed. 13.The vehicle speed control system according to claim 12 wherein the lowerthe speed at which the vehicle is travelling or the lower the targetset-speed, the smaller the incremental value.
 14. The vehicle speedcontrol system as claimed in claim 10, further comprising an automaticterrain mode selector comprising a plurality of vehicle and/orenvironmental sensors and configured to select an automatic terrain modein dependence upon said vehicle and/or environmental sensors, andwherein said incremental value is dependent upon a signal indicative ofthe automatically selected terrain mode.
 15. A vehicle comprising avehicle speed control system as claimed in claim
 1. 16. The vehiclespeed control system according to claim 1 wherein said at least oneelectronic controller further controls the vehicle control speed as afunction of the terrain over which the vehicle is travelling.
 17. Amethod of automatically controlling the speed of a vehicle having aplurality of wheels at a vehicle control speed in dependence on an inputtarget set-speed, the method comprising: receiving a user input of atarget set-speed at which the vehicle is intended to travel; applying atorque to the at least one of the plurality of wheels for propelling thevehicle at the vehicle control speed; controlling the vehicle controlspeed as a function of at least the instantaneous vehicle speed,evaluating the torque to be applied to at least one of the vehiclewheels and outputting a torque request signal; and reducing the vehiclecontrol speed in dependence on the torque request signal.
 18. The methodaccording to claim 17 further comprising controlling the vehicle controlspeed as a function of the terrain over which the vehicle is travelling.19. A non-transient carrier medium carrying a computer readable code forcontrolling a vehicle to automatically control the speed of the vehicleto a vehicle control speed in dependence on an input target set-speed,wherein the computer readable code, when executed by an electronicprocessor, causes the processor to: receive an electrical signalindicative of a user input of a target set-speed at which the vehicle isintended to travel; apply a torque to the at least one of the pluralityof wheels for propelling the vehicle at the vehicle control speed;control the vehicle control speed as a function of at least theinstantaneous vehicle speed; evaluate the torque to be applied to atleast one of the vehicle wheels and outputting a torque request signal;and reduce the vehicle control speed in dependence on the torque requestsignal.